386 - Multicellular Animals, Especially Man 



permeated with blood sinuses, and ordinarily, 

 when the sinuses are not distended with 

 blood, the tissue is flaccid. But one of the 

 reflexes in the pattern of sexual excitation 

 leads to a constriction of the vessels that 

 drain the sinuses. At this time, therefore, the 

 erectile tissue becomes turgid and distended 

 with blood; and temporarily the penis be- 

 comes an effective intromittent organ. When 

 ejaculation occurs, the urethra is swept by a 

 short but powerful series of peristaltic con- 

 tractions. 



THE FEMALE REPRODUCTIVE ORGANS 



The ovaries, in vertebrate animals, are not 

 connected directly with the oviducts. In the 

 frog, for example, each large ovary or egg 

 mass, lies in the bod)' cavity, ventral to the 

 corresponding kidney (Fig. 21-4). The ostium, 

 or dilated mouth of the oviduct, opens di- 

 rectly into the body cavity in a region some- 

 what anterior to the ovary (Fig. 21-4). To be 

 liberated, therefore, the eggs must break 

 through the wall of the ovary and pass 

 through the body cavity to the ostium. This 

 rupturing of the ovarian wall is referred to 

 as ovulation, and after ovulation the eggs 

 are carried to the mouth of the oviduct by 



the activity of the ciliated epithelium that 

 lines the peritoneal cavity. 



The eggs of the frog do not possess any 

 external coating of "jelly" before they enter 

 the oviduct; but while an egg is passing 

 through the oviduct it receives its "jelly coat" 

 from gland cells lining the wall. Like the 

 sperm duct, the oviduct of the frog leads to 

 the cloaca rather than to the exterior, and 

 the eggs are finally voided through the cloacal 

 opening. Just before joining the cloaca, the 

 oviduct shows a slightly expanded section, 

 called the "uterus" (Fig. 21-4). However, no 

 development occurs while the eggs remain in 

 this part of the oviduct, and consequently 

 the term uterus is not a very apt one. 



True copulation does not occur in the 

 frog, but an analogous reaction, called am- 

 plexus (Fig. 21-8), takes place about 24 hours 

 before the female starts to shed the eggs. 

 Amplexus continues until all the eggs have 

 been extruded into the water; and simul- 

 taneously the male continues to liberate a 

 stream of sperm while the eggs are issuing 

 forth. 



The Human Ovary and Its Functions. In 

 the human female, as in other vertebrates, 

 the ovaries have no direct connection with 

 the oviducts, or Fallopian tubes. The human 



F!g. 21-8. Amplexus, in toads. (Courtesy of Roberts Rugh, Columbia University.) 



